1. Field of the Invention
This invention relates to a materials handling machine and more particularly to a self-propelled forklift machine having improved front end stability for carrying heavy loads as encountered in hauling materials and equipment in underground mining operations.
2. Description of the Prior Art
Materials handling machines, such as forklift units are well known in the art for transporting heavy loads by a forklift unit pivotally connected by boom arms and powered by hydraulic tilt cylinders to the front end portion of a self-propelled tractor or the like. U.S. Pat. No. 3,115,261, 3,312,361, 3,458,069 and 3,706,388 are illustrative of this type and are adapted for use with earth moving tractors. Also it is known to utilize a hydraulic lift cylinder for vertically raising and lowering the forklift unit relative to the mobile frame. With this arrangement, the tines in a lowered position are advanced by tramming the machine into position to receive the load. Thereafter, the loaded unit may be moved vertically and tilted backwardly for positioning the load for tramming.
One problem encountered in carrying loads by a forklift unit is the load limitation which the unit can carry because of the torsional loads which are imposed by a loaded forklift unit on the piston rod of the lift cylinder. If the loads become excessive, the forces exerted upon the piston rod can bend the piston rod in the cylinder or destroy the packing around the piston rod which causes the cylinder to leak and a reduction in lifting capability of the cylinder.
In addition, as encountered with maneuvering heavy loads by a self-propelled forklift unit, the mobile frame becomes unstable. This occurs primarily when a heavy load is carried too far forward of the front axle, placing a moment on the front end of the frame and reducing the stability of the load. In some cases the traction of the rear wheels on the roadway is reduced by placing a heavy load on the forklift unit. This is particularly the case for vehicles of long longitudinal dimension.
In underground mining operations a number of lifting and hauling operations are encountered in moving equipment and materials throughout the mine. For example in moving longwall mining equipment from panel to panel in the mine requires substantial time in order to disassemble, move and reassemble the longwall unit. Items such as cribbing, hydraulic props, face conveyor components, shield type supports and the like varying in weight from a few tons to many tons must be moved. Due to the confined working area of a mine, the means for transporting the items must be easily maneuverable and highly stable.
While it has been suggested by the prior art to utilize forklift units for large material handling operations, there is need for a forklift type materials handling machine adaptable for use in underground mining operations where heavy loads can be transported without damage to the hydraulic lift cylinder and the load is positioned as close as possible to the front axles of the mobile frame.